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Synthesis and reactivity of solids from ‘mild’ to ‘severe’ chemistry for ‘smart’ materials
Current Opinion in Solid State and Materials Science 4 (1999) 109–111
Editorial overview
Synthesis and reactivity of solids from ‘mild’ to ‘severe’ chemistry for ‘smart’ materials ´ a , *, A.J. Jacobson b G. Ferey a
Institute Lavoisier, Universite´ de Versailles St. Quentin, 45, avenue des Etats-Unis, 78035 Versailles Cedex, France b University of Houston, Department of Chemistry, Houston, Texas 77204 -5641, USA
At the end of the 20th century, both western and Asian governments have come to understand that there is a strong relation between economic growth and progress in materials science. It has been estimated that in developed countries, this branch of science (including electronic, magnetic, optical, catalytic and environmental materials) contributes directly or indirectly, through processes and products, to some 30–40% of the Gross Domestic Product. The continuously increasing demand from industry for tailored materials for specific applications leads materials scientists to improve the performance of known systems and to create new solids with enhanced properties. This challenge provides a driving force for innovation, the discovery of new phases and for new techniques and approaches to chemical synthesis. From the beginning of the fifties, synthesis in materials science was mainly associated with reactions at high temperatures and / or pressures. The combination with crystallography and physics within the ‘golden triangle’ of synthesis-structure-properties provided rules for prediction, principally for thermodynamically stable solids. Synthesis at high temperatures and pressures continues to be an important approach and has provided in the last 10 years important families of materials like the high T c superconductors and colossal magneto-resistance materials. The introduction in the eighties, however, of the concepts of ‘chimie douce’ and of sol–gel processes opened the way for new pathways including low temperature reactions and the use of solutions. Solubilization-precipitation phenomena combined with acid–base and redox chemistry give rise to new families of inorganic or hybrid organic–inorganic materials when organic species are introduced as
*Corresponding author. ´ [email protected] E-mail addresses: [email protected] (G. Ferey), (A.J. Jacobson)
reactants. Compared with solid–solid reactions in which diffusion processes govern the nature of the product, solution media allow different approaches to the synthesis and modification of solids. Among the materials obtained in this way, microporous, mesoporous and low dimensional solids have become of importance in catalysis, separations and environmental applications. The articles in this issue illustrate the effort and imagination of chemists in the creation of new materials, modification of their properties and to approach an understanding of their formation. The last point is key if new materials are to be designed and tailored with appropriate properties for specific applications. The title of this overview indicates that the papers in this issue cover a wide spectrum of synthetic approaches. Mild chemistry is described in the papers of Ozin et al. (pp. ´ 113), Beltran-Porter et al. (pp. 123), Xu (pp. 133), and ¨ Muller et al. (pp. 141). These reviews concern mainly liquid–solid reactions of organic–inorganic systems at low temperatures and / or under hydrothermal conditions. Both molecular and solid state approaches lead to numerous molecular, microporous, mesoporous and low dimensional materials. For the latter, beautiful exfoliation / re-assembly processes using polymers and pillars are applied. The severity of the chemistry increases through the final three papers. Keszler (pp. 155) and Battle and Rosseinsky (pp. 163) use traditional medium or high temperature methods for the synthesis of metal borates and manganates with a strong emphasis on the coupling between properties, composition and detailed structure. McMillan (pp. 171) and to a lesser extent Ozin et al. (pp. 113) with the fullerenes and nanotubes, give recent news of very high pressure / very high temperature synthesis. All of these materials are relevant to direct or ‘smart’ applications in strategic areas such as superconductors, CMR, catalysis, energy, non-linear optical devices and super-hard materials.
1359-0286 / 99 / $ – see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-0286( 99 )00010-8
110
´ , A. J. Jacobson / Current Opinion in Solid State and Materials Science 4 (1999) 109 – 111 G. Ferey
In the mild chemistry part, emphasis is placed on ¨ ´ chalcogenides (Ozin, Muller), phosphates, (Beltran-Porter) ¨ and molybdates (Xu, Muller). Except in the paper by ¨ Muller which will be discussed further below, the use of inorganic and organic templates in the syntheses of porous or low-dimensional materials is reviewed. It is often claimed that porous solids originate from the condensation of molecular clusters around templates which are sometimes inorganic cations and often protonated or neutral amines. Templates and clusters are two key points in this part of the issue. The influence of variations in organic templates on the formation of many different structure types is well illustrated by Xu (pp. 133) in the discussion of new families of molybdates. The templating effect is ´ still not well understood and Beltran-Porter et al. take the opportunity in their review to introduce an interesting discussion of this subject. They take into account the reaction variables and basic concepts of solution chemistry in examining the relations between the topology of the materials and the nature and scale of the precursors: cations, molecules or supramolecular templates. The latter lead to new mesoporous vanadium phosphates. Mesostructures of tin, germanium and zinc sulfides and their use in electro-optical displays and chemical sensing applications are also discussed by Ozin et al. (pp. 113). The major part of their review, however, is concerned with microporous metal chalcogenides and the clusters from which they are built up via corner-sharing. Indeed, with tin, germanium and indium open framework solids are formed from different building blocks: Sn 2 S 6 , Sn 3 S 4 , adamantoid M 4 S 10 and with indium, superadamantoid In 20 S 20 for which an SN2 mechanism is postulated for the condensation polymerization of the clusters. The size of the clusters is another key point. From hydrothermal reactions, several questions arise. How do they form? Do they pre-exist in solution? What is the driving force that governs their size? In situ techniques including NMR [1] under hydrothermal conditions, not covered in this issue, begin to give an answer to these questions. Control of the size of the building blocks, probably related to some parameters of the templates, can lead to very open frameworks. The larger the clusters, the larger the pores, and a paper by Li et al. [2] describes two structures based on [In 10 S 20 ] 10— clusters with cavities of ˚ (cages) and 14.7 A ˚ (tunnels) in diameter, the In–S 25.6 A framework corresponding to only 25% of the volume. ¨ Muller et al. propose another and controlled way to reach this goal. Using supramolecular chemistry, they are able to build up giant ring-shaped polyoxometallates (molybdenum or tungsten) containing up to 248 metallic atoms. They show that these ring-shaped clusters can be used as synthons to form compounds with layer and chain structures. Moreover, they show that the internal part of the ring-shaped cluster can be used as a nanoreactor in which smaller Mo clusters are formed within the wheel whose topology is related to some bulk molybdenum
oxides. This poses some general questions concerning ¨ nucleation of solids. Muller goes further into this problem of clusters as sections of solid state structures with examples of metal chalcogenides in which the increasing size of the clusters progressively results in a topology close to that of the extended solid. All of these papers show the richness of this field and the questions that arise in the synthesis of materials with very open frameworks. Alternative approaches include the emerging synthesis of hybrid materials in which the organic and inorganic parts belong to the skeleton [3] but the major need now is to develop an understanding of the processes involved though a major effort in physical chemistry. High temperature synthesis of two important classes of metal oxides are described in the reviews by Keszler (pp. 155) and Battle and Rosseinsky (pp. 163). Keszler reviews the current state-of-the-art on the synthesis, the crystal chemistry, the materials processing (thin films, single crystals) and the optical properties of metal borates. Research in this area is an active field of study and the number of new compounds and new structure types continues to grow. Recent advances in the chemistry of borate phosphate, borate fluorides and polyborates are discussed together with their applications as luminescent, nonlinear optical and laser materials. Battle and Rosseinsky provide a detailed overview of the current understanding of the magnetic behavior of the n52 layered Ruddlesden and Popper manganates (III, IV). They analyze the differences between the layered compounds and the corresponding three-dimensional perovskites in terms of structure, cation ordering and electrical and magnetic properties. In particular, the complexity of the layered materials with respect to cation distributions, intergrowths, structural modulations and subtle phase separation effects as revealed by high resolution X-ray diffraction, neutron diffraction and electron microscopy is highlighted. They emphasize that a detailed understanding of the magnetism and the magneto-transport in these phases will only be obtained after further careful control of the synthetic chemistry in relation to defect and phase equilibria. The most ‘severe’ chemistry is represented by high pressure / high temperature synthesis. High pressure techniques are still relatively unexplored for the synthesis of inorganic materials with unusual structures and properties but the area has received new and increasing interest. McMillan (pp. 171) describes highlights in the area during the past two years. Emphasis is placed first on super-hard materials like diamond, C 3 N 4 , icosahedral borides, and high hardness forms of carbon obtained by polymerizing C 60 and C 70 . The recent contribution of high pressure techniques (including synthesis with reactive gases and supercritical fluids) to the study of high T c superconductors, GMR, high dielectric constant oxides, chalcogenides and pnictides is also analyzed.
´ , A. J. Jacobson / Current Opinion in Solid State and Materials Science 1 (1999) 109 – 111 G. Ferey
This overview reinforces the importance of imagination in chemical synthesis for providing new solids and concepts in materials science with the aim of finding new applications. Despite a continuous effort to understand the relations between structural evolution and properties of solids, empiricism often remains the rule. Progress in the discipline now needs a combination of new discoveries with an improved mechanistic approach to the formation of solids. This overview represents some recent steps towards achieving this goal.
111
References ´ [1] Haouas M, In-Gerardin C, Taulelle F, Estournes C, Loiseau T, Ferey G. NMR of microporous compounds: from in situ reactions to solid pairing. Colloids and Interfaces A; in press. [2] Li H, Laine A, O’Keeffe M, Yaghi OM. Supertetrahedral sulfide crystals with giant cavities and channels. Science 1999;283:1145– 147. [3] Chui SS-Y, Lo SM-F, Charmant JPH, Orpen AG, Williams ID. A chemically functionalizable nanoporous material [Cu 3 (TMA) 2 (H 2 O) 3 ]. Science 1999;283:1148–150.
Editorial overview
Synthesis and reactivity of solids from ‘mild’ to ‘severe’ chemistry for ‘smart’ materials ´ a , *, A.J. Jacobson b G. Ferey a
Institute Lavoisier, Universite´ de Versailles St. Quentin, 45, avenue des Etats-Unis, 78035 Versailles Cedex, France b University of Houston, Department of Chemistry, Houston, Texas 77204 -5641, USA
At the end of the 20th century, both western and Asian governments have come to understand that there is a strong relation between economic growth and progress in materials science. It has been estimated that in developed countries, this branch of science (including electronic, magnetic, optical, catalytic and environmental materials) contributes directly or indirectly, through processes and products, to some 30–40% of the Gross Domestic Product. The continuously increasing demand from industry for tailored materials for specific applications leads materials scientists to improve the performance of known systems and to create new solids with enhanced properties. This challenge provides a driving force for innovation, the discovery of new phases and for new techniques and approaches to chemical synthesis. From the beginning of the fifties, synthesis in materials science was mainly associated with reactions at high temperatures and / or pressures. The combination with crystallography and physics within the ‘golden triangle’ of synthesis-structure-properties provided rules for prediction, principally for thermodynamically stable solids. Synthesis at high temperatures and pressures continues to be an important approach and has provided in the last 10 years important families of materials like the high T c superconductors and colossal magneto-resistance materials. The introduction in the eighties, however, of the concepts of ‘chimie douce’ and of sol–gel processes opened the way for new pathways including low temperature reactions and the use of solutions. Solubilization-precipitation phenomena combined with acid–base and redox chemistry give rise to new families of inorganic or hybrid organic–inorganic materials when organic species are introduced as
*Corresponding author. ´ [email protected] E-mail addresses: [email protected] (G. Ferey), (A.J. Jacobson)
reactants. Compared with solid–solid reactions in which diffusion processes govern the nature of the product, solution media allow different approaches to the synthesis and modification of solids. Among the materials obtained in this way, microporous, mesoporous and low dimensional solids have become of importance in catalysis, separations and environmental applications. The articles in this issue illustrate the effort and imagination of chemists in the creation of new materials, modification of their properties and to approach an understanding of their formation. The last point is key if new materials are to be designed and tailored with appropriate properties for specific applications. The title of this overview indicates that the papers in this issue cover a wide spectrum of synthetic approaches. Mild chemistry is described in the papers of Ozin et al. (pp. ´ 113), Beltran-Porter et al. (pp. 123), Xu (pp. 133), and ¨ Muller et al. (pp. 141). These reviews concern mainly liquid–solid reactions of organic–inorganic systems at low temperatures and / or under hydrothermal conditions. Both molecular and solid state approaches lead to numerous molecular, microporous, mesoporous and low dimensional materials. For the latter, beautiful exfoliation / re-assembly processes using polymers and pillars are applied. The severity of the chemistry increases through the final three papers. Keszler (pp. 155) and Battle and Rosseinsky (pp. 163) use traditional medium or high temperature methods for the synthesis of metal borates and manganates with a strong emphasis on the coupling between properties, composition and detailed structure. McMillan (pp. 171) and to a lesser extent Ozin et al. (pp. 113) with the fullerenes and nanotubes, give recent news of very high pressure / very high temperature synthesis. All of these materials are relevant to direct or ‘smart’ applications in strategic areas such as superconductors, CMR, catalysis, energy, non-linear optical devices and super-hard materials.
1359-0286 / 99 / $ – see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-0286( 99 )00010-8
110
´ , A. J. Jacobson / Current Opinion in Solid State and Materials Science 4 (1999) 109 – 111 G. Ferey
In the mild chemistry part, emphasis is placed on ¨ ´ chalcogenides (Ozin, Muller), phosphates, (Beltran-Porter) ¨ and molybdates (Xu, Muller). Except in the paper by ¨ Muller which will be discussed further below, the use of inorganic and organic templates in the syntheses of porous or low-dimensional materials is reviewed. It is often claimed that porous solids originate from the condensation of molecular clusters around templates which are sometimes inorganic cations and often protonated or neutral amines. Templates and clusters are two key points in this part of the issue. The influence of variations in organic templates on the formation of many different structure types is well illustrated by Xu (pp. 133) in the discussion of new families of molybdates. The templating effect is ´ still not well understood and Beltran-Porter et al. take the opportunity in their review to introduce an interesting discussion of this subject. They take into account the reaction variables and basic concepts of solution chemistry in examining the relations between the topology of the materials and the nature and scale of the precursors: cations, molecules or supramolecular templates. The latter lead to new mesoporous vanadium phosphates. Mesostructures of tin, germanium and zinc sulfides and their use in electro-optical displays and chemical sensing applications are also discussed by Ozin et al. (pp. 113). The major part of their review, however, is concerned with microporous metal chalcogenides and the clusters from which they are built up via corner-sharing. Indeed, with tin, germanium and indium open framework solids are formed from different building blocks: Sn 2 S 6 , Sn 3 S 4 , adamantoid M 4 S 10 and with indium, superadamantoid In 20 S 20 for which an SN2 mechanism is postulated for the condensation polymerization of the clusters. The size of the clusters is another key point. From hydrothermal reactions, several questions arise. How do they form? Do they pre-exist in solution? What is the driving force that governs their size? In situ techniques including NMR [1] under hydrothermal conditions, not covered in this issue, begin to give an answer to these questions. Control of the size of the building blocks, probably related to some parameters of the templates, can lead to very open frameworks. The larger the clusters, the larger the pores, and a paper by Li et al. [2] describes two structures based on [In 10 S 20 ] 10— clusters with cavities of ˚ (cages) and 14.7 A ˚ (tunnels) in diameter, the In–S 25.6 A framework corresponding to only 25% of the volume. ¨ Muller et al. propose another and controlled way to reach this goal. Using supramolecular chemistry, they are able to build up giant ring-shaped polyoxometallates (molybdenum or tungsten) containing up to 248 metallic atoms. They show that these ring-shaped clusters can be used as synthons to form compounds with layer and chain structures. Moreover, they show that the internal part of the ring-shaped cluster can be used as a nanoreactor in which smaller Mo clusters are formed within the wheel whose topology is related to some bulk molybdenum
oxides. This poses some general questions concerning ¨ nucleation of solids. Muller goes further into this problem of clusters as sections of solid state structures with examples of metal chalcogenides in which the increasing size of the clusters progressively results in a topology close to that of the extended solid. All of these papers show the richness of this field and the questions that arise in the synthesis of materials with very open frameworks. Alternative approaches include the emerging synthesis of hybrid materials in which the organic and inorganic parts belong to the skeleton [3] but the major need now is to develop an understanding of the processes involved though a major effort in physical chemistry. High temperature synthesis of two important classes of metal oxides are described in the reviews by Keszler (pp. 155) and Battle and Rosseinsky (pp. 163). Keszler reviews the current state-of-the-art on the synthesis, the crystal chemistry, the materials processing (thin films, single crystals) and the optical properties of metal borates. Research in this area is an active field of study and the number of new compounds and new structure types continues to grow. Recent advances in the chemistry of borate phosphate, borate fluorides and polyborates are discussed together with their applications as luminescent, nonlinear optical and laser materials. Battle and Rosseinsky provide a detailed overview of the current understanding of the magnetic behavior of the n52 layered Ruddlesden and Popper manganates (III, IV). They analyze the differences between the layered compounds and the corresponding three-dimensional perovskites in terms of structure, cation ordering and electrical and magnetic properties. In particular, the complexity of the layered materials with respect to cation distributions, intergrowths, structural modulations and subtle phase separation effects as revealed by high resolution X-ray diffraction, neutron diffraction and electron microscopy is highlighted. They emphasize that a detailed understanding of the magnetism and the magneto-transport in these phases will only be obtained after further careful control of the synthetic chemistry in relation to defect and phase equilibria. The most ‘severe’ chemistry is represented by high pressure / high temperature synthesis. High pressure techniques are still relatively unexplored for the synthesis of inorganic materials with unusual structures and properties but the area has received new and increasing interest. McMillan (pp. 171) describes highlights in the area during the past two years. Emphasis is placed first on super-hard materials like diamond, C 3 N 4 , icosahedral borides, and high hardness forms of carbon obtained by polymerizing C 60 and C 70 . The recent contribution of high pressure techniques (including synthesis with reactive gases and supercritical fluids) to the study of high T c superconductors, GMR, high dielectric constant oxides, chalcogenides and pnictides is also analyzed.
´ , A. J. Jacobson / Current Opinion in Solid State and Materials Science 1 (1999) 109 – 111 G. Ferey
This overview reinforces the importance of imagination in chemical synthesis for providing new solids and concepts in materials science with the aim of finding new applications. Despite a continuous effort to understand the relations between structural evolution and properties of solids, empiricism often remains the rule. Progress in the discipline now needs a combination of new discoveries with an improved mechanistic approach to the formation of solids. This overview represents some recent steps towards achieving this goal.
111
References ´ [1] Haouas M, In-Gerardin C, Taulelle F, Estournes C, Loiseau T, Ferey G. NMR of microporous compounds: from in situ reactions to solid pairing. Colloids and Interfaces A; in press. [2] Li H, Laine A, O’Keeffe M, Yaghi OM. Supertetrahedral sulfide crystals with giant cavities and channels. Science 1999;283:1145– 147. [3] Chui SS-Y, Lo SM-F, Charmant JPH, Orpen AG, Williams ID. A chemically functionalizable nanoporous material [Cu 3 (TMA) 2 (H 2 O) 3 ]. Science 1999;283:1148–150.